C.C.
I think we feel this way because his work touched us on a personal level. He made us laugh in a way that few others ever have. Everyone has a memory of Robin Williams that's special. For me, I remember watching his stand-up comedy special on HBO when I was 37 weeks pregnant with my first child. I laughed SO hard at his bit on how the Scots invented golf that I went into labor. Not even kidding! I found the clip on YouTube last night and showed it to my kids - it was every bit as funny now as it was then.
For anyone who hasn't seen it... http://www.youtube.com/watch?v=xDQd49rEF_0